In a conventional image processing system, a position information apparatus transmits to a master apparatus the detection position of a control subject as a position-detection signal, through a transmission line, an image processing apparatus starts image processing, in accordance with a start command from the master apparatus, and an image-processing signal obtained through the image processing is transmitted to the master apparatus. As a prior art such as this, Patent Reference 1 below is known.    (Patent Reference 1) Japanese Laid-Open Patent Publication No. 1998-320021